Replaceable element tr tube



May 7, 1957 F. A. LESCH REPLACEABLE ELEMENT TR TUBE 3 Sheets-Sheet W a A m w w m m A y 1957 F. A. LESCH 2,791,720

REPLACEABLE ELEMENT TR TUBE Filed Nov. 26, 1956 3 Sheets-Sheet 2 4 INVENTOR. FEPDINAND A. LESCH UG paga ATTOZNEY y 1957 F. A. LESCH 2,791,720

REPLACEABLE ELEMENT TR TUBE Filed Nov. 26, 1956 3 Shets-Sheet 3 INVENTOR. FEEDINAND A. LESCH ATTOIZNEY REPLACEABLE ELEMENT TR TUBE i Ferdinand A. Lesch, Beverly, Mass., assignor to Bomac Laboratories Inc., Beverly, Mass., a corporation of Massachusetts The present invention relates broadly to gaseous discharge ultra high frequency switching devices and more specifically to a novel structure incorporating both the capacitive and inductive elements in a unitary device adapted to be mounted in rectangular waveguide to form together with an encapsulated window a complete transmit-receive tube.

The embodiment of the invention is commonly employed in microwave radar systems to protect the receiver by means of a highly attenuating gaseous discharge within a waveguide structure when the transmitter is pulsing. During the receive cycle the signal energy will be permitted to pass to the receiver unattenuated. Examples of prior art transmit-receive `or TR devices incorporating the capacitive cone structure defining a discharge gap and inductive metallic members are illustrated in the text Microwave Duplexers by L. D. Smullin and C. G. Montgomery, McGraw-Hill Book Co., New York, 1948, pages 67-70 and 106-112. With the structure therein described contained within a hermetically sealed envelope such prior art devices are commonly filled with an ionizable atmosphere under reduced pressure. It is in the selection of this atm-osphere that prior art transmit-receive tubes involve a series of compromises in the desirable electricalparameters such as spike leakage energy, fiat leakage power, recovery time and arc loss.

Ionizable gases such as hydrogen or argon generally are' combined with a small amount of -water vapor to enhance the electron capturing properties *of the gas in order to improve recovery time. However, this gas filling increases the leakage power and arc less values. In addition, certain mechancal disadvantages result from oxidation of the internal metallic comp onents or corrosion of the hermetically sealed joints of the overall waveguide envelope. A further disadvantage eXists in that with prior 'art construction, certain light-.weight metals such as aluminum cannot be employed for the waveguide assembly because of the large variance in the coeicent of expansion `of such metals and the dielectric materials used for the window seals.

The primary object of the present invention, therefore, is to provide a novel transmt-receive tube in which each resonant element is provided with its own internal gas fill selected for the 'optimum electrcal characteristics.

A further object is to provide a novel transmit-receive tube with separable and interchangeable resonant elements which are replaceable individually without necessitating replacement of the entire tube with an acc-ompanying saving in costs.

'A still further `object is to provide individual replaceable TR cells each possessing the inductive and capacitive Components of a complete resonant circuit together with an encapsulated structure to permit the use of separate gas fillings.

Another 'object is to provide individual replaceable resonant elements to form collectively a TR tube in which each element contains its own gas filling enclosed within a dielectric enclosure to eliminate the disadvantages of nited States Patent O laten edrM y "7, 1,957:

i prior art devices wherein thegas filling is enclosed within in a section of hollow pipe rectangular waveguide. The

first important resonant element `is the input window which is provided with a frame member defining `a dielectric enclosed -aperture of conventional Construction A trough member of a dielectric material is mounted on one side to completely encapsulate this structure and provide an enclosure containing a gaseous atmosphere selected to optimize the recovery time and arc loss characteristics. i Spaced within the waveguide section at the conventional quarter-wavelength distance are individual integral resonant cell assemblies eonstructed in accord-v ance with the teachings of the present invention. Each cell includes capacitive electrode members enclosed within a dielectric envelope with inductive elements disposed coaxially on either side of this encapsulated structure; The top and bottom members of the complete assembly are designed to make good electrc contact when mounted in the waveguide section. Clamping means engage the top member to retain the assembly in operative position. The individual cells are provided with a gas fill within the enclosure, however, in this instance such parameters as spike leakage energy and flat leakage power are of primary concern and watervapor may be eliminated Each cell may further be provided with an ignter electrode structure of well known Construction. Although onlyone *of the cells need be connected to a suitable direct current source to facilitate partal i onization of the gas, the provision of the igniter electrode in all cells permits interchangeability or replacement during operation without the removal of the overall wavegude assembly from the system. Furthermore, the igniter top cap provides a convenient means for handling of the individual cells duringthe mounting operation.

,in usage the need for maintenance of large inventories of prior art tubes is eliminated sinceonly the individual cells need be stocked. This will result in virtual elimination of lost or down 'tmein demounting of complete tube assemblies as well as considerable savings in replacement' costs. i

Other 'objects, advantages and features will be evident attenconsideration of the followingdetailed specificatio and the appended drawings, in which:

Fig. 1 is a perspective view of the illustrative embodiment showing one 'of the replaceable cells in position for mounting;

Fig. 2 is an enlarged side view of the embodiment with the resonant Window in perspective and a portion of the wavegude removed to reveal the mounted resonant cell assembly;

Fig. 3 isan enlarged cross-sectional view of the resonant input window assembly; and

`Fig. 4 is an enlarged cross-sectonal view of the replaceable cell asse-mbly of the embodiment. i

Referringnow to Figs. 1 and 2, the illustrative embodiment of a complete broadband TR tube incorporating all demountable elements is shown and comprises a sec.- tion of hollow pipe waveguide 1 with mounting flanges 2 and3`sealed-at the ends thereof. The resonant input; window assembly shown-generally at 4 may be simply mounted at one end by screw fastening means Secured to the narrowside of the window assembly with the ends of the fastening means shown at 5. Threaded apertures 6 of the assembly matewith similar apertures in the flange 2 along the broadside to facilitate mounting of the overall. tube in a waveguide system. i The demountable resonant cell assembly 7 is shown` iri' position 'for mounting in the waveguide 1 by means of a threaded clamping base 8 secured to the top wall of the waveguide. A contact sleeve 9 is secured to the opposte wall of the waveguide 1 to receive the lower portions of the cell assembly. To assure accurate positioning of the cell without any subsequent rotation, a key 10 is provided in sleeve 9 with a groove 11 in the cell bottom. After the cell has been inserted a teflo n washer 12 and metal ring 13 are positioned within base 8 and a clamping ring 14 retains the cell in position.

Turning now to Fig. 2 the output end of the tube will be seen. According to the teachings of the inventon it will no longer be necessary to evacuate and fill the overall waveguide 1 and, therefore, a flat metallic plate 15 is sealed within flange 3. A resonant aperture 16 is centrally provided within plate 15 and the conventonal hermetically sealed dielectric enclosure maybe omitted.

One of the features of the present nvention resides in' the use of light weight metals since critical glass-tometal seals necessary in the prior art to provide a vacuum tight tube have been elminated. It is, therefore, desirable to fabricate flanges 2 and 3, waveguide 1 and metallic plate 15 from aluminum stock such as 61S-'1`6 instead of the conventional brass and steel found in prior art tubes.

The resonant encapsulated window assembly 4 will now be described in detail by referring to Fig. 3. A relatively short section of Waveguide 17 has brazed thereto a flange 18 which will mate with flange 2 of the tube assembly. Metal plate 19 is secured to section 17 and is provided with a resonant iris covered with a dielectric enclosure 20 of the conventional construction. The inner surface of plate 19 s heavily glazed in the area ndicated at 21 with a beaded powdered glass suspension and a glass trough 22 formed from glass tubing is 'heat sealed to this glazed side. Trough 22 is provided with an exhaust stem 23 through which the complete encapsulated assembly may be evacuated and filled with the desired gaseous atmosphere. In an illustrative embodiment a filling of millmeters of argon was employed with a relatively small percentage of water vapor added to enhance the recovery time characteristics. If desired, quartz wool may also be positioned within the glass trough in the manner well known in the art.

The complete window assembly may then be provided with a wire mesh gasket 24 to provide for good electrical contact when the tube is mounted in wavegude structure.

The demountable resonant cell assembly 7 is shown in detail in Fig. 4 and comprises a top cylindrical member 25 having a hub portion 26 and a flanged portion 27. A thin disc collar 28 of a highly conductive metal such as copper is secured to the fiange 27. A lower cylindrical member 29 is axially disposed from member 25 and comprises a flange 30, a portion 31 of reduced cross section, and a still narrower section 32 terminating in a substantially conical point 32A to define one of the gap electrodes. A passageway 33 extends axially through this member with apertures 34 provided in the walls of 'portion 32 to facilitate evacuation of the complete cell assembly. A glass cylinder 35 is hermetically sealed at its ends to hub portion 26 and portion 31 of member 29 to define a gas tight envelope.

'To complete the gap electrode structure of the capacitive resonant circuit of the overall cell a combined screw type electrode with an igniter electrode is provided according to the teachings of U. S. Patent No. 2,524,268 issued October 3, 1950 to Henry J. McCarthy. In the embodiment a hollow conical tip screw 36 with an open end-is threaded into the hub portion 26 until the desired spacing from tip 32A is achieved to tune the cell assembly to a predetertm'ned resonant frequency. Nut 37 and Washer 38 lock the screw in the tuned position. An igniter electrode 39 of standard construction is positioned within screw 36 and is supported by means of collar 40 and glass bead *41. Top cap 42 provides means for connection to a direct current voltage supply. Spacer 43 is secured to member 25 to support the igniter electrode collar 40. The inductive Components of the resonant circuit of the overall cell assembly comprise a pair of rod members 44 and 45 supported between flanges 27 and 30 and securely fastened therein. The provision of these inductive members as a part of the demountable cell assembly eliminate the need for the conventional fiat metallic plate structures generally found in TR devces.

A multi-fingered resilient contact ring 46 is secured to member 29 to provide for positive engagement of the overall cell assembly within sleeve 9 when the assembly is inserted in the waveguide 1. Exhaust tube 47 is also secured within the hollow portion of member 29 in alignment with passage 33 to provide for eVa-cuation of the cell envelope. An appropriate gaseous atmosphere may then be introduced into the cell. Since the electrical considerations for this Component of the overall tube are primarily spike leakage energy and flat leakage power, a different gas fill may be employed from that of the encapsulated window. In this embodirnent approximately four and one half millmeters of argon and one millimeter of hydrogen was found to yield the most Satisfactory results. After filling, the exhaust tubulation may be tipped-o, sealed and a protector cover 48 inserted as shown.

The complete tube assembly comprisirg one or more of the resonant cell assemblies and an encapsulated input window each having its own integral gas fill provides a unique device over prior art tubes in that replacernent of individual Components may be easily accomplshed. This results in cost savings since under prior art design the complete tube including expensive metal envelopes must be replaced when electrical characteristics exceed or fall below one or more of the specified requirements. A further advantage resides in the fact that cell assemblies may be replaced without disturbing the Waveguide system set up.

With the structure disclosed the problem of metallic sputtering under fired conditions of intense ionization is considerably reduced since all gaseous discharges are confined within dielectric enclosures. As a result it is now possible to use combinations of metals and gases which were heretofore noncompatible. Aluminum is therefore desirable for all metallic Components not requiring a high coefficient of expansion to match that of glass. This light weight metal aids in reducing the overall system weight which is particularly desirable in airborne radar systems.

While a specific illustrative embodiment has been described it will be evident to skilled artisans that various modifications may be incorporated. An example may be the provision of a tuning mechanism within the cell assembly in place of the fixed tuned structure disclosed in the specification.

What is claimed is:

l. An ultra high frequency gaseous discharge switch ing device comprising a metallic Waveguide envelope, a demountable encapsulated resonant window assembly disposed at one end of said Waveguide envelope with an apertured plate member sealed at the opposite end thereof, a unitary demountable composite resonant circuit member spaced at intervals of approximately one-quarter of a wavelength within said waveguide envelope, said resonant circuit member including both the capacitive and inductive elements with the capacitive elements enclosed within a dielectric envelope and an individual filling of a gaseous atmosphere contained within said window assembly and dielectric envelope.

2. An ultra high frequency gaseous discharge switching device comprising a section of metallic rectangular waveguide, a demountable encapsulated resonant window assembly positioned at one end of said wavegude section, a metallic plate member having a central resonant aperture secured at the opposite end thereof, a demountable resonant cell assembly spaced at intervals of approximately one-quarter of a wavelength within said waveguide section, said cell assembly including capacitive discharge gap electrode structure enclosed within a dielectric envelope and inductive elements positioned parallel to said capacitive electrode structure and an individual filling of a gaseous atmosphere contained within said window assembly and dielectric envelope.

3. An ultra high frequency gaseous discharge switching device comprising a section of hollow rectangular waveguide, a demountable encapsulated resonant window assembly positioned at one end of said waveguide section, a metallic plate member having a central resonant aperture secured at the opposite end thereof, a demountable resonant cell assembly spaced at intervals of approximately one-quarter of a wavelength within said waveguide section, said resonant cell assembly comprising an upper and lower member with metallic inductive members supported therebetween, said upper and lower members each definng a capacitive electrode with said electrodes being in axial alignment and spa-ced apart to provide a discharge gap, a dielectric envelope enclosing said capacitive discharge gap electrodes and a filling of a gaseous atmosphere contained within said dielectric envelope.

4. An ultra high frequency gaseous discharge device comprising a section of hollow rectangular waveguide, a demountable gas-filled encapsulated resonant window assembly positioned at one end of said waveguide section, a metallic plate member having a central resonant aperture secured at the opposite end thereof, a demountable resonant cell assembly spaced at intervals of approximately one-quarter of a wavelength within said waveguide section, said resonant cell assernbly comprising an upper and lower member each supporting a substantially conical electrode with said electrodes being in axial alignment and oppositely disposed to define a discharge gap, a cylindrcal dielectrc member hermetically sealed to said upper end lower member to thereby encapsulate said discharge gap in a vacuum tight enclosure and filling of a gaseous atmosphere contained within said enclosure, a flanged portion provided on each of said upper and lower members and a pair of metallic members secured to and extending between said flanged portions.

5. An ultra high frequency gaseous discharge switching device comprsing a section of hollow rectangular waveguide having a pluralty of spaced aligned apertures disposed in the upper and lower broad walls along the longitudinal axis -thereof, a demountable gas-filled encapsulated resonant window assembly positioned at one end of said waveguide section, a metallic plate member having a central resonant aperture secured at the opposite end thereof, a demountable gas-filled resonant cell assembly mounted in said waveguide section and extending between each pair of aligned waveguide apertures, said resonant cell assenbly having means for engaging the walls of said apertures to thereby provide good electrical contact, said cell assembly further providing in a unitary structure the capacitive and inductive elements of a composite resonant circuit when mounted in the waveguide section.

6. A transmit-receve tube comprising a section of rectangular Waveguide having postioned theren a plurality of unitary resonant cell assemblies adapted to be interchanged with one another or removed for replacement, each of said cell assemblies comprising a top cylindrical member having a flanged section and a central axial passageway, a threaded conical tipped metallic member extending through said aXial passageway, a bottom cylindrical member having a fianged section and a central portion of reduced cross-section terminating in a substantially conical tip, metallic posts secured to said fianged sections to thereby maintain said 'top and bottom members in spaced relationship with said conical tips being oppositely disposed to define therebetween a capacitive discharge gap, dielectric enclosure means joined to said top and bottom members to enclose said discharge gap and a filling of an ionizable atmosphere contained within said enclosure, a demountable gas-filled encapsulated resonant window assembly enclesing one end of said Waveguide section and a fiat metallic member with a central resonant aperture hermetically sealed to the opposite end of said waveguide section.

7. A transmit-receive tube comprsing a section of rectangular waveguide of a lightweight metal having positioned therein a plurality of demountable resonant cell assembles, each of said cell assemblies comprisng an upper and lower fianged member connected together by a pair of cylindrical posts joined thereto near the peripheral edge of the fianges, capaeitive discharge gap electrode structure oppositely disposed from and supported by said upper and lower members, a dielectric envelope enclosing said electrode structure and a filling of an 'nert gaseous atmosphere contained therein, an encapsulated resonant window assernbly containing a gaseous atmosphere and water vapor removably secured to one end of the waveguide section and a plate member having a central resonant opening permanently secured at the opposite end, said plate member being selected from the same metal as said waveguide section.

References Cited in the file of this patent' UNITED STATES PATENTS 2,587,305 Fiske Feb. 26, 1952 2,631,255 Stavro Mar. 10, 1953 2,680,207 Booth June 1, 1954 2,748,351 Varnern May 29, 1956 

